• Put the cauliflower, onion and stock in a large heavy saucepan. Bring to the boil, cover and simmer for about 15 minutes until soft. • Add the milk and walnuts, and stir through. Purée in a blender or food processor until smooth.• Return the soup to the pan. Season to taste with salt and pepper, then bring to the boil – be careful not to scorch. Serve hot.